Peter Farrelly has never turned up his nose at total silliness, directing such raunchy comedies such as There’s Something About Mary and Dumb and Dumber with his brother Bobby. But collaborating as one of a dozen directors on the upcoming ensemble comedy Movie 43 had its own unique perks, not the least of which was getting to see a slew of A-list stars such as Naomi Watts and Kate Winslet let loose.

The movie, set to release Jan. 25, 2013, has a cast and story as celebrity-steeped and plot-twisty as a Robert Altman film crossed with the shameless spunkiness of Jackass. In addition to Watts and Winslet, it includes appearances by: Elizabeth Banks, Halle Berry, Kate Bosworth, Gerard Butler, Kieran Culkin, Josh Duhamel, Anna Faris, Chris Pratt, Richard Gere, Terrence Howard, Hugh Jackman, Johnny Knoxville, Chloe Moretz, Justin Long, Leslie Bibb, Liev Schreiber, Seann William Scott, Emma Stone, Jason Sudeikis, and Uma Thurman. Whoosh, that’s a mouthful. With all those actors, more than 15 writers, and several directors, including Farrelly and actress Banks herself, the movie took several years to make.

“It’s the brainchild of Charlie Wessler, who produced most of our movies. Never before have such huge actors pushed the envelope so much,” said Farrelly by phone. “Charlie knows all these people. He went to them, huge stars, like Kate Winslet, and she said, ‘I’m shooting this movie, I’m not free for a year and a half.’ This movie was made over four years, and they just had to wait for a year or two years for different actors. They would shoot for a week, and shut down for several months. Same thing with the directors. It was the type of movie you could come back to.”

While there’s a major plot line that Farrelly won’t yet reveal, what we can share is that all the actors, such as dramatic movie queens Watts and Winslet, abandoned themselves to pure comedy in varying, divergent story lines with an R-rated slant. Watts flashes some 1980s flair as a borderline psycho mom, alongside her real-life love Liev Schreiber, as parents who homeschool their son, played by Shameless co-star Jeremy Allen White, but completely subject him to school bullying (a bratty Watts with a teenage side ponytail, priceless). Winslet goes on a blind date with Hugh Jackman and learns he has a weird birth defect. Freak-outs ensue. Terrence Howard coaches a 1950s all-black basketball team, giving the players pieces of advice definitely not considered PC. Halle Berry, looking as model gorgeous as ever, goes against type by playing a saucy game of truth or dare in a restaurant with erstwhile Ricky Gervais collaborator Stephen Merchant. Two words: turkey baster.

Farrelly, who directed the parts of the movie with Berry and Winslet, joked about reactions to a serious Oscar winner such as Winslet doing a 180, with perfect comic timing.

“I spoke at Harvard last year with my brother Bobby. People always ask if we’re going to do a dramatic movie, so we said we just did, with Kate Winslet, and told them, ‘Let’s show a little clip,’” said Farrelly. “People were so stunned. I don’t think an audience at Harvard has ever laughed that hard. There’s the fact that Kate Winslet had the balls to just go for it.”

As for recently Tweeting about writing a sequel to the Jim Carrey and Jeff Daniels 1994 hit Dumb and Dumber, Farrelly confirmed that the script was coming along.

“We’re finishing the script right now, and we’re moving ahead as if it’s happening,” said Farrelly. “I’m extremely happy about it. Nothing is firm yet, but we’re extremely happy.”